Wind Turbine Nacelle, Transport System for a Wind Turbine Nacelle and Method for Transporting a Wind Turbine Nacelle

ABSTRACT

A wind turbine nacelle is provided. The wind turbine nacelle includes a longitudinal extension and a bottom part. The longitudinal extension has a rear end and a front end. At the bottom part, an opening is located which serves as an interface to a tower of a wind turbine at a designated assembly situation of the nacelle. A first detachable leg arrangement is attached to at least one of the front end and the rear end. A second detachable leg arrangement is attached at the bottom part. Further embodiments are directed to a transport system for a wind turbine nacelle and to a method for transporting a wind turbine nacelle.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority of European Patent Office applicationNo. 10165733.6 EP filed Jun. 11, 2010, which is incorporated byreference herein in its entirety.

FIELD OF INVENTION

The present invention concerns a wind turbine nacelle with alongitudinal extension with a rear end and a front end and with a bottompart at which there is located an opening serving at a designatedassembly situation of the nacelle to be an interface to a tower of awind turbine. It also concerns a transport system for a wind turbinenacelle and a method of transporting such wind turbine nacelle.

BACKGROUND OF INVENTION

The transport of large wind turbine components such as nacelles or towersegments by lorry or other earth-bound vehicles is usually quitecomplicated. Due to the large load, in particular the weight of suchwind turbine components, it is usually necessary to use cranes in orderto load or unload large wind turbine components onto or down from suchvehicles. Such loading or unloading by crane makes the procedure verycomplicated and also expensive.

In addition, it is necessary to ensure that the height of the means oftransport combined with the height of the transported load does notexceed certain height limits which are due to bridges and/or tunnelsthat are to be passed on the way. This is a particular challenge whentrying to transport wind turbine nacelles. Most particularly directdrive nacelles comprising a direct drive generator are very large indiameter (about up to 6 metres) so that keeping the transport heightsmaller than the given limits is currently sometimes impossible and someother routes or even other means of transport have to be chosen instead.Reduction of combined height is thus a very important task.

Yet another problem is caused when the wind turbine component is takenoff the earth-bound transport vehicle e.g. onto a ship: This normallyimplies that two different fixing system to fix the wind turbinecomponent to the respective means of transport need to be used.

It is known from EP 1622792 B1 to suspend a wind turbine component inbetween a trailer and a dolly using standardisation means at either endof the wind turbine component. These standardisation means are thenconnected to the trailer and to the dolly. This system may in fact berealised in such way that the above-mentioned obstacles arecircumvented. However, by transporting a wind turbine component in thisway, the component becomes a part of the vehicle itself as it connectsthe trailer and the dolly. Therefore, forces inflicted onto thetransport vehicle during transport may damage the wind turbinecomponent.

SUMMARY OF INVENTION

This is a problem for wind turbine nacelles in particular. They usuallyhave a smaller length but a bigger height than a tower segment and theyare made of a less stable material than tower segments. In addition,they have a more irregular structure than tower segments because theycomprise an opening in the bottom part which forms an interface with thetower. Therefore, the same forces might not seriously affect a towersegment while they might be quite dangerous to a nacelle.

It is therefore the object of the invention to provide the possibilityfor a wind turbine nacelle to be transported and/or to be supplied fortransport in a way that best suits both the circumstances of transport,in particular the height limits, and at the same time makes suchtransport safer for the wind turbine nacelle itself.

This object is met by the features of the independent claims.

Therefore, a wind turbine nacelle of the above-mentioned kind isenhanced by attaching a first detachable leg arrangement to the frontend and/or the rear end and by attaching a second detachable legarrangement at the bottom part. Thereby, the second detachable legarrangement is preferably partially inserted into the opening.

The first detachable leg arrangement and the second detachable legarrangement may be different in shape and even material and may alsocomprise different kinds of legs. A leg arrangement may comprise onlyone leg for instance but may also comprise two or more legs as well,depending on the transport necessities. In general, it can be consideredto be any kind of arrangement upon which the wind turbine nacelle can bepositioned such that it rests stably on the ground in the region of theleg arrangement. This means, that a leg arrangement can also be any kindof solid foot having a much wider extension in one or more directionsthan would be usually known in the context of legs. It may thus alsogenerally be called a positioning means.

Such positioning of leg arrangements, on the one hand at either thefront and or the rear end (or in fact either ends) and on the other handvia the bottom part, makes sure that the nacelle is positioned on theground in a highly stable way which ensures that it can be transportedby only inflicting forces onto the leg arrangements instead of ontoparts of the nacelle itself. Furthermore, the attachment of the legarrangements to the nacelle and in fact the attachment of fixing meansto fix the leg arrangements to a means of transport may be realised attwo different levels of height above ground. At a first height level,the first leg arrangement is affixed to the nacelle, at a second heightlevel the second leg arrangement is affixed to the nacelle. Accordingly,the first leg arrangement can also be connected to a means of transportat a first connection level and the second leg arrangement can beconnected to the same means of transport at a second connection level.This also implies that—as will be shown below—transport and thepreparation for transport of such wind turbine nacelle is by far easierthan used to be the case. As for the use of the opening at the bottompart for attachment of the second leg arrangement, this gives an extraadvantage in the sense that the second leg arrangement can be firmlypositioned at the bottom part without any particular extra effort, inparticular with no fixing means attached to the outside shell of thenacelle in the region of the bottom part. This particular arrangement ofconstruction also implies that the nacelle can be positioned at aminimum distance from the ground despite the fact that the second legarrangement is positioned at the bottom part of it. A stable connectionbetween a leg arrangement and the bottom part of the nacelle wouldusually imply a certain added height of overall. By including part ofthe leg attachment inside of the nacelle through the bottom part openingthis height can be considerably reduced.

To sum up, a wind turbine nacelle according to the invention has theadvantage of high stability, little extra height due to the legarrangements and optionally the possibility to suspend it at differentsuspension levels at the same time.

According to the invention a transport system for a wind turbinenacelle, in particular a wind turbine nacelle according to the inventionas described before, comprises a first trailer and a second trailerinterconnected by a bridge assembly, the bridge assembly being realizedsuch that in an assembled state it indirectly holds the nacelle by beingfixed to a first leg arrangement and to a second leg arrangement whileat the same time forming a stable frame which can be suspended inbetween the first trailer and the second trailer.

Such transport system includes the leg arrangements attached to the windturbine nacelle, which are usually used for positioning the nacelleabove ground. To this end, a bridge assembly is used which holds boththe first leg arrangement and the second leg arrangement fixedly. Thisbridge assembly also forms a stable frame. The expression “stable” isused for such frames which bear the forces inflicted upon them duringtransport from the side of the first trailer and/or from the secondtrailer. This means that these forces will not be led further into theleg arrangements and eventually to the wind turbine nacelle itself, orat least they will be considerably reduced so that there is no danger ofinjuries to the nacelle. This makes sure that the wind turbine nacelleis not put under unnecessary stress. In other words, the bridge assemblyis both a holding means for the two leg arrangements and a stabiliserand buffer with respect to forces which occur during transport.

As for the definition of “trailer”, it should be noted that thisexpression may include both trailers suspended on a supporting vehiclesuch as a tractor and so-called dollies. A trailer may also comprise atraction means of its own or—as preferred—be pulled by means of atractor, which eliminates a lot of weight for the incorporation of atraction means and its power supply. According to a preferredembodiment, one of the trailers is a dolly and the other one either atrailer interconnected with a tractor or a tractor itself. It may alsobe noted, that the bridge assembly and either of the first and secondtrailers may have parts which can be assigned to both of them. Forinstance, the bridge assembly would not typically be considered to havewheels on its underside, but it may have in the context of theinvention. In this sense, the bridge assembly may take over thefunctions of a dolly which might make a second trailer realised as adolly unnecessary. In the context of the invention such a constructionwould be considered such that the bridge arrangement and the secondtrailer are not separated in terms of parts—as is however preferably thecase in order to simplify separation and handling—but only in terms offunctions.

According to the invention, a method of transporting a wind turbinenacelle of the aforementioned kind comprises the following steps:

a) attaching a first detachable leg arrangement to the front end and/orthe rear end,b) attaching a second detachable leg arrangement at the bottom part,c) fixing a bridge assembly to the first leg arrangement and to thesecond leg arrangement in such way that the bridge assembly forms astable frame which can be suspended in between a first trailer and asecond trailer of a transport system,d) connecting the bridge assembly to the first and second trailer,e) optionally raising the bridge assembly.

In the first two steps the wind turbine nacelle is prepared fortransport in such way that it becomes a wind turbine nacelle accordingto the invention. In the following steps this nacelle is then fixed tothe transport system according to the invention in a way that makespossible a safe transport. In order to reach such state it may also benecessary to raise the bridge assembly so that the wind turbine nacelleis also raised. In particular this means that the first and second legarrangements will be raised above ground so that they do not stand onthe ground during transport. With respect to transport heights it may benoted however, that it is not necessary to lift the wind turbine nacelleand the bridge assembly very far above ground. In particularly criticalcircumstances during transport, it is even possible to lower the bridgeassembly with the wind turbine nacelle to an absolute minimum level inorder to be able to pass a passage which otherwise would not bepossible. In fact, as described above, the height of the transportsystem can be realized only slightly bigger than the height of the windturbine nacelle on its own positioned on the two leg arrangements. Ashas also been described above, the extra height due to the two legarrangements can be very little as well because the second legarrangement can be positioned in the opening of the bottom part. Thefirst leg arrangement can also be realized in such way that it adds aslittle extra height as the second leg arrangement.

Particularly advantageous embodiments and features of the invention aregiven by the dependent claims, as revealed in the following description.Thereby, features revealed in the context of the nacelle and/or thenacelle may also be realized in the context of the respective other andin the context of the transport method.

As for the wind turbine nacelle according to the invention of there aretwo particularly advantageous embodiments:

Firstly it is particularly preferred that the first leg arrangementcomprises a frame part projecting essentially in longitudinal directionfrom the rear end or front end at which the first leg arrangement islocated, the frame part being positioned above ground when the windturbine nacelle is placed on the ground via at least the first legarrangement, the frame part being realized such that it is stable enoughfor a raising force from below sufficient to raise the wind turbinenacelle at the rear end or front end at which the first leg arrangementis located.

Such a frame part projects from the leg arrangement in the directionwhich is essentially perpendicular to the vertical direction whichdefines that direction in which the nacelle is positioned on the ground.Thus it may be considered to be a kind of extra part only attached tothe first leg arrangement. This frame part can be used as that part ofthe first leg arrangement at which fixing means of the bridge assemblywill be attached. Instead of positioning the bridge assembly underneaththe leg arrangement—which would be quite a normal use of a legarrangement—it can now be fixed at a different point, i.e. the framepart, instead.

According to a second preferred embodiment, the second leg arrangementcomprises a fixing region elevated from the ground when the wind turbinenacelle is placed on the ground via at least the second leg arrangement.In this context it is particularly preferred that the fixing regioncomprises legs which project in a horizontal direction. At these legsparts of the bridge assembly can be affixed from the side of thenacelle, i.e. perpendicular to its longitudinal extension. Suchattachment along with the longitudinal extension of the nacelle isparticularly easy to realize, again in comparison with an attachment ofthe bridge assembly at the bottom part of the second leg arrangement.Furthermore, it is not necessary to lift the second leg arrangementprior to connecting it with the bridge assembly, which again makeshandling much easier and procedures quicker and in fact cheaper.

Turning now to the transport system itself, preferred embodiments referparticularly to the bridge assembly.

Preferably, the bridge assembly comprises a first longitudinal beam anda second longitudinal beam arranged essentially in parallel in anassembled state of the bridge assembly such that in between the firstlongitudinal beam and the second longitudinal beam the first and/or thesecond leg arrangement is fixed. The first longitudinal beam and thesecond longitudinal beam are preferably at least as long as thelongitudinal extension of the nacelle to be transported. This means thatthey can be arranged along the complete extension of the nacelle. Inthis sense, a longitudinal beam comprising several beam partsinterconnected with each other would also be considered to be one singlelongitudinal beam. Whereas the longitudinal beams may fix both the firstand second leg arrangement in between them, it is more preferred thatthey only fix one leg arrangement by direct contact. This implies thatthe other leg arrangement which is not fixed directly by thelongitudinal beams will be fixed by a different kind of measure, whileit is preferred that the longitudinal beams and such other kind ofmeasure are interconnected in some way. This way the other legarrangement is indirectly connected to the longitudinal beams. Suchembodiment provides some extra safety guarantee for the overall fixingof the nacelle system (comprising the nacelle itself and the legarrangements).

In particular it is preferred that the second leg arrangement is fixedby the longitudinal beams. For instance, in combination with a fixingregion as described above projecting sideways from the longitudinalextension of the nacelle, such fixing of the second leg arrangement tothe longitudinal beans may be realised by using the fixing regions andby putting them into orifices of the longitudinal beams.

This implies, which is a particularly preferred embodiment of thetransport system according to the invention, that the first and/orsecond leg arrangement is fixed in between the first longitudinal beamand the second longitudinal beam by a foil', fitting, which is an easyway of connecting those two elements without additional tools and extraforce for fixing.

Such fixing may be realised for example if the first longitudinal beamand/or the second longitudinal beam is a beam which comprises at leastat one position in a cross section an upper end section and a lower endsection and a middle section in between, which upper end section and/orlower end section has a larger horizontal extension perpendicular to thelongitudinal extension of the beam than the middle section so that thefirst and/or second leg arrangement is held in the region of the middlesection in between the upper end section and the lower end section. Forinstance, the longitudinal beams may have a cross section shaperesembling an H or a IT turned round by 90°. Along the middle sectionthere is thus formed an orifice into which parts of the respective legarrangement can be inserted.

Another option, which can be combined with the previous and also be usedon its own, is that the first longitudinal beam and/or the secondlongitudinal beam is a beam with a middle section with at least oneopening into which the first and/or second leg arrangement fits at leastone of its ends. This particular end of the leg arrangement, forinstance the fixing region mentioned before, can then be inserted intothe opening of the first and/or second longitudinal beam. Again, this isan easy way of connecting the leg arrangement with the beam.

In addition, the bridge assembly preferably comprises a cross beamorientated essentially perpendicularly to the longitudinal extension ofthe bridge assembly. Such cross beam can interconnect the aforementionedlongitudinal beams and either be permanently affixed to them,temporarily affixed or even just laid upon them. Such crossbeam makessure that the frame structure of the bridge assembly is held in thecross direction as well. According to a particularly preferredembodiment the cross beam is, in an assembled state of the bridgeassembly, positioned such that the first and/or second leg arrangementis positioned on the cross beam via a frame part which is part of thefirst and/or second leg arrangement. Such frame part may for instance bethe frame part mentioned before in the context of the particularlypreferred embodiment of the wind turbine nacelle. In other words, thecrossbeam and the frame part mentioned before form another connectionbased on the form fitting principle which is reliable in this particularcontext.

A particularly advantageous solution in this context is to position thecross beam such that the first leg arrangement is positioned on it. Thefirst leg arrangement then rests upon the cross beam which means thatthe full weight of about half the nacelle rests upon this cross beam. Inreturn the cross beam will be connected to the rest of the bridgeassembly by means of the force resulting from this weight. However, itis still preferred to interconnect the cross beam with the rest of thebridge assembly by fixing means such as bolts.

In a preferred embodiment of the transport system the bridge assemblycomprises several separate construction parts (such as the longitudinalbeams and the cross beam) which are detachably interconnected in anassembled state. This way the construction parts can be assembled aroundthe nacelle and dense to leg arrangements. This means that the nacellewith its leg arrangements does not need to be lifted onto the bridgearrangement, but rather the bridge arrangement is built around it. Thisresults in a reduction of effort and costs.

As has been mentioned before, it is often necessary to raise the nacelleand/or the bridge assembly before heading off for transport. For thatpurpose the transport system preferably comprises a raising meanscapable of raising the bridge assembly from a loading position into atransport position and back.

In order to make sure the transport system according to the inventioncan be used for numerous systems of wind turbine nacelles of today andof future generations and in consideration of the fact that the bridgeassembly may be constructed around such wind turbine nacelle, theinventors have found it to be particularly advantageous that thetransport system comprises adaption means for adapting the extensions ofthe bridge assembly to the size of the nacelle to be transported. Forinstance such adaption means may include prolongations of longitudinalbeam is and/or cross beams or the possibility to add extra length tothese beams by any other means. This is way different wind turbinenacelles of different sizes can still be transported with the sametransport system, also in the future.

Other objects and features of the present invention will become apparentfrom the following detailed descriptions considered in conjunction withthe accompanying drawings. It is to be understood, however, that thedrawings are designed solely for the purposes of illustration and not asa definition of the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numbers refer to like objectsthroughout. Objects in the diagrams are not necessarily drawn to scale.

FIG. 1 shows a side view of a nacelle according to an embodiment of theinvention,

FIG. 2 shows the view of the same nacelle as in FIG. 1 seen from thefront end of the nacelle,

FIG. 3 shows the view of the same nacelle as in the previous figuresfrom the rear end of the nacelle,

FIG. 4 shows a section view of the same nacelle as in the previousfigures along a vertical section in the longitudinal direction of thenacelle,

FIG. 5 shows a section view of the same nacelle as in the previousfigures along a line V-V depicted in FIG. 1,

FIG. 6 shows an embodiment of a transport system according to theinvention in a side view with the same nacelle as in the previousfigures,

FIG. 7 shows a detailed top view of the bridge assembly shown in FIG. 6,

FIG. 8 shows a section view along a line VIII-VIII as shown in FIG. 7,

FIG. 9 shows a schematic block diagram of principal steps of anembodiment of a transport method according to the invention.

DETAILED DESCRIPTION OF INVENTION

FIGS. 1 to 5 show a wind turbine nacelle 1. Referring in particular toFIG. 1, the nacelle 1 has a longitudinal extension with a front end Band a rear end A. The nacelle 1 has a bottom part 5 in which there is anopening 3. A first leg arrangement 9 is attached at the front end B ofthe nacelle 1 and a second leg arrangement 7 is attached at the bottompart 5. More specifically, the second leg arrangement 7 is inserted intothe opening 3.

The leg arrangement 9 is bolted to the front end B of the nacelle 1,i.e. in a region in which the hub of the rotor (not shown) of the windturbine will be fixed later. The leg arrangement 9 (cf. FIG. 2)comprises two legs which end in a semi circular carrier structure 10. Inthe region of the carrier structure 10 the leg arrangement 9 is boltedtemporarily to the front end B of the nacelle 1. The leg arrangement 9has a main vertical extension. However, at the side facing away from thefront end B off the nacelle 1 there is attached a frame part 11 whichprojects away from the front end B and which forms a kind of additionalfoot above ground level underneath which a crossbeam 13 is positioned,which can be used to raise the nacelle 1 at its front end B.

The second leg arrangement 7 comprises two cross beams 7 a, 7 b withfixing rings 19. Onto the crossbeams 7 a, 7 b a tubular structure 23 isfixed. Flanges 21 attached to the tubular structure 23 lead through thefixing rings 19 in order to provide for a fixing of the tubularstructure 23 to the crossbeams 7 a, 7 b.

Some of the details shown in FIG. 1 can be clearer understood when goingalong FIGS. 2 to 5.

For instance, in FIG. 2, which shows a look at the front end B of thenacelle 1, there are also depicted two longitudinal beams 35, 37underneath the cross beam 13 which serve to carry the cross beam 13 inthe context of a bridge assembly which will be explained later (cf. FIG.7).

In FIGS. 3 and 5 the shape of the tubular structure 23 is easier toperceive. From the perspective of the view at the rear end of thenacelle 1 (cf. FIG. 3) it can be seen that the tubular structure 23 isbasically made up like the tower of a wind turbine, however withcut-outs 26 both at the end facing into the direction of the rear end Aof the nacelle 1 and at the other end facing into the direction of thefront end B of the nacelle 1. As can be seen in FIG. 4, the cut-outs 26divide the tubular structure 23 into two halves interconnected by aconnecting beam 24. Both in FIG. 3 and FIG. 4 it can be seen that thecross beams 7 a, 7 b do not end with a vertical end structure, butrather with a diagonal one. These end structures constitute a fixingregion which is partially elevated from the ground, the reason of whichwill be explained with reference to FIG. 8.

FIG. 4 shows the nacelle 1 in a longitudinal section view. As can beseen here in particular, the leg arrangement 7 is orientated such thatthe tubular structure 23 is inserted into the opening 3 in a similar wayas the end of a wind turbine tower. Orifices 25 in the tubular structure23 serve as openings into which the crossbeams 7 a, 7 b are inserted.

FIG. 6 shows an embodiment of a transport system 27 according to theinvention. It comprises a first trailer 29 and a second trailer 31 inbetween which a bridge assembly 33 is suspended. The first trailer 29 isattached to a tractor 30 at the front end of the transport system 27.The second trailer 31 is realised as a dolly, i.e. without any driveunit of its own. On the bridge assembly 33 the nacelle 1 of thepreceding figures is loaded. The bridge assembly 33 comprises a firstlongitudinal beam 35 and a second longitudinal beam (not shown in thisperspective), as well as the cross beam 13 as mentioned in the contextof FIG. 1.

Full views of the bridge assembly 33 are depicted in FIGS. 7 and 8.

FIG. 7 shows the bridge assembly 33 in a top view. It comprises twoparallel longitudinal beams 35, 37. Assembled in parallel upon them in aperpendicular orientation there are cross beams 13, 39. The longitudinalbeams 35, 37 and the crossbeams 13, 39 make up components which can befixed to one another and taken apart later again. In the context of thebridge assembly 33 according to the transport system 27 of FIG. 6, thecrossbeams 7 a, 7 b of the second leg arrangement 7 (cf. FIG. 1) projectinto the longitudinal beams 35, 37, so that they are fixed in betweenthem.

This can be better seen in FIG. 8, which is a section view along a lineVIII-VIII in FIG. 7. Both the longitudinal beam 35 and the longitudinalbeam 37 have top regions 35 a, 37 a and bottom regions 35 c, 37 c, whichare interconnected by middle regions 35 b, 37 b. As both longitudinalbeams 35, 37 are thus realized as profiled beams with thecross-sectional shape of a II turned over by 90°, orifices 35 d, 37 dare fanned into which the cross beam 7 a is inserted at either ends. Itsshape at either ends is such that they define a fixing region asmentioned above, i.e. partially elevated from the ground so that thelongitudinal beams 35, 37 can be brought underneath the cross beam 7 afrom the side with little effort.

FIG. 9 shows a schematic block diagram of an embodiment of a transportmethod according to the invention. For that purpose, a wind turbinenacelle 1 is equipped in the way shown in FIG. 1. For that purpose, in afirst step Z the first leg arrangement 9 is attached to the front end Bof the nacelle 1 and in a second step Y the second leg arrangement 7 isattached at the bottom part 5 in the opening 3 to build a nacelle 1according to the invention. Then, in a third step X, the bridge assembly33 is connected to the first leg arrangement 9 and to the second legarrangement 7 as shown in FIG. 6. The bridge assembly 33 thus forms astable frame. In a fourth step W the bridge assembly 33 is connected tothe first trailer 29 and to the second trailer 31 as also shown in FIG.6. Eventually, in an optional fifth step V, the bridge assembly 33 israised by raising means incorporated in the first trailer 29 and/or inthe second trailer 31 (both raising means not shown). The nacelle 1 cannow be moved and is held stably by the bridge assembly 33.

Although the present invention has been disclosed in the form ofpreferred embodiments and variations thereon, it will be understood thatnumerous additional modifications and variations could be made theretowithout departing from the scope of the invention. While a particularshape of leg arrangements and bridge assembly was used as a basis forthe description, the transport system and the nacelle according to theinvention may be realized in many other ways suitable for the particularsize and transport necessities of a specific case.

For the sake of clarity, it is to be understood that the use of “a” or“an” throughout this application does not exclude a plurality, and“comprising” does not exclude other steps or elements.

1.-15. (canceled)
 16. A wind turbine nacelle, comprising: a longitudinalextension comprising a rear end and a front end; a bottom part at whichthere is located an opening which serves as an interface to a tower of awind turbine at a designated assembly situation of the nacelle; a firstdetachable leg arrangement attached to at least one of the front end andthe rear end; and a second detachable leg arrangement attached at thebottom part.
 17. The wind turbine nacelle according to claim 16, whereinthe second detachable leg arrangement is partially inserted into theopening.
 18. The wind turbine nacelle according to claim 16, wherein thefirst detachable leg arrangement comprises a frame part projectingessentially in a longitudinal direction from the rear end or front endat which the first detachable leg arrangement is located, wherein theframe part is positioned above ground when the wind turbine nacelle isplaced on the ground via at least the first detachable leg arrangement,and wherein the frame part is realized such that it is stable enough fora raising force from below sufficient to raise the wind turbine nacelleat the rear end or front end at which the first detachable legarrangement is located.
 19. The wind turbine nacelle according to claim16, wherein the second detachable leg arrangement comprises a fixingregion elevated from the ground when the wind turbine nacelle is placedon the ground via at least the second detachable leg arrangement.
 20. Atransport system for a wind turbine nacelle, comprising: a firsttrailer; a second trailer; and a bridge assembly interconnecting thefirst trailer and the second trailer, the bridge assembly being realizedsuch that in an assembled state it indirectly holds the nacelle by beingfixed to a first leg arrangement and to a second leg arrangement whileat the same time forming a stable frame which can be suspended inbetween the first trailer and the second trailer.
 21. The transportsystem according to claim 21, wherein the bridge assembly comprises afirst longitudinal beam and a second longitudinal beam arrangedsubstantially parallel to each other in an assembled state of the bridgeassembly such that at least one of the first leg arrangement and thesecond leg arrangement is fixed in between the first longitudinal beamand the second longitudinal beam.
 22. The transport system according toclaim 21, wherein the at least one of the first leg arrangement and thesecond leg arrangement is fixed in between the first longitudinal beamand the second longitudinal beam by form fit.
 23. The transport systemaccording to claim 21, wherein at least one of the first longitudinalbeam and the second longitudinal beam is a beam comprising, at least atone position in a cross section, an upper end section, a lower endsection and a middle section between the upper and lower end sections,wherein at least one of the upper end section and the lower end sectionhas a larger horizontal extension perpendicular to the longitudinalextension of the beam than the middle section so that the at least oneof the first leg arrangement and the second leg arrangement is held in aregion of the middle section in between the upper end section and thelower end section.
 24. The transport system according claim 21, whereinthe at least one of the first longitudinal beam and the secondlongitudinal beam is a beam with a middle section having at least oneopening into which the at least one of the first leg arrangement and thesecond leg arrangement fits at least one of its ends.
 25. The transportsystem according to claim 20, wherein the bridge assembly comprises across beam orientated essentially perpendicularly to a longitudinalextension of the bridge assembly.
 26. The transport system according toclaim 25, wherein the cross beam is, in an assembled state of the bridgeassembly, positioned such that at least one of the first leg arrangementand the second leg arrangement is positioned on the cross beam via aframe part, the frame part being a part of the at least first legarrangement and the second leg arrangement.
 27. The transport systemaccording to claim 26, wherein the cross beam is positioned such thatthe first leg arrangement is positioned on it.
 28. The transport systemaccording to claim 20, wherein the bridge assembly comprises a pluralityof separate construction parts which are detachably interconnected in anassembled state.
 29. The transport system according to claim 20, furthercomprising a raising device for raising the bridge assembly from aloading position into a transport position and back.
 30. The transportsystem according to claim 20, further comprising an adaption device foradapting an extension of the bridge assembly to the size of the nacelleto be transported.
 31. A method of transporting a wind turbine nacelle,the wind turbine nacelle comprising a longitudinal extension with a rearend and a front end and a bottom part, wherein, at the bottom part islocated an opening serving at a designated assembly situation of thenacelle to be an interface to a tower of a wind turbine, the methodcomprising: attaching a first detachable leg arrangement to at least oneof the front end and the rear end; attaching a second detachable legarrangement at the bottom part; fixing a bridge assembly to the firstleg arrangement and to the second leg arrangement in such way that thebridge assembly forms a stable frame which can be suspended in between afirst trailer and a second trailer of a transport system; and connectingthe bridge assembly to the first trailer and the second trailer.
 32. Themethod according to claim 31, further comprising raising the bridgeassembly.